Streams draining urban areas are affected by ecological degradation, revealed by symptoms as flashier hydrographs, elevated concentrations of nutrients and contaminants, altered channel morphology, and reduced biotic richness, with increased dominance of tolerant species. The urban stream syndrome is a consequence of multiple, co-occurring and interacting stressors difficult to disentangle and assess individually. We assessed the effects of water and food from two origins (urban vs. forest stream) on the consumption and survival of nymphs of highly intolerant (IBMWP score 10) aquatic insects of the genera Leuctra (Ephemeroptera) and Sericostoma (Trichoptera). Larvae were kept in water, either from an urban or a forest stream and fed with alder leaves, previously incubated either in the urban or in the forest stream water, in a total of four treatments. Consumption rates of urban food were higher than consumption rates of control food, and higher in the urban than in the forest stream water. In the case of the Plecoptera, the highest consumption rates resulted in the highest increase in body mass and earlier eclosion, suggesting a compensatory feeding mechanism. This may be due to deficient microbial colonization of the leaves incubated in urban stream water resulting in lower food-value. However, a larger experimental set and longer period trial must be carried out in order to disentangle the effects of water quality from other factors potentially causing the lack of intolerant aquatic insect species in urban streams.

SS12 – Presentation

Leaf litter decomposition along the longitudinal profile of a temporary Mediterranean stream: spatial and seasonal variability

Temporary rivers and streams are the dominant watercourses in Mediterranean regions and their spatial extent is expected to increase worldwide as a result of ongoing global change. However, these systems are a recent addition to freshwater ecology and their highly heterogeneous structure is far from that considered in classical paradigms. Consequently, there is an urgent need to better understand the ecology of these systems, and to this end, it is essential to consider their temporal and spatial heterogeneity due to flow variation. Our aim was to describe leaf litter decomposition along the longitudinal profile of a temporary Mediterranean stream with high variability in flow conditions (perennial lentic, perennial lotic and intermittent) in two contrasting seasons: winter and summer. We used coarse- and fine-mesh bags containing Populus nigra leaves to examine changes in decomposition rates, litter quality and decomposer communities. Our results indicated that large fluctuations in flow along the stream were accompanied by large fluctuations in leaf litter decomposition. In winter, dry and emerged conditions on intermittent reaches resulted in lower decomposition rates than in perennial reaches. In summer, an unexpected increase in precipitation events enhanced differences in flow along the stream. Local conditions modulated the inundation regime of intermittent reaches, resulting in higher decomposition rates in the more inundated one, similar to rates in permanently flowing reaches. To better understand the functioning of highly heterogeneous environments such as temporary streams, we should assume their structure as a changing mosaic of contrasting habitats and characterized their conditions properly.

SS02 – Presentation

Threats and opportunities of integrating ecosystem services in nature management

Ecosystem services have become a mainstreaming topic in the research and policy agendas, and their relevance in nature management is dramatically increasing. Many have raised concerns on their use, as valuing nature from a utilitarian point of view might suppose a serious threat on biodiversity. Here, we review current knowledge on the relationship between biodiversity, ecosystem function, socio-economy, and monetary values of ecosystem services, discussing some of the most influential and less considered factors in this triangle: valuation strategy, services use and demand, individual revealed and stated preferences, and the spatial and temporal dimensions. After this review, we discuss the opportunities offered by the integration of ecosystem services in nature management that minimize the previously discussed threats on biodiversity: integrated management for human wellbeing and biodiversity, linkage of artificial and natural management elements, replacement of traditional grey infrastructures by nature-based solutions, and improvements in the life-cycle assessments in the framework of circular economy.

SS04 – Poster

Effects of warming and grazer distribution on riverine eutrophication control

Benthic filter feeders (BFF) can reduce phytoplankton density thereby controlling eutrophication in shallow aquatic ecosystems, including rivers. However, the efficiency of eutrophication control depends on abiotic and biotic factors such as water depth, BFF distribution and initial phytoplankton concentration (hereafter: Pin value). Furthermore, experiments suggest that warming can alter eutrophication control by grazers by shifting the relationship between BFF grazing rate and the growth rate of planktonic prey. To test how such control changes with temperature under the influence of water depth, Pin value, BFF density and spatial BFF distribution, we developed a spatially-explicit simulation model. Our model includes the thermal responses of BFF grazing and phytoplankton growth. Results show that BFF grazing can qualitatively alter and, under some conditions, reverse phytoplankton response to warming. Moreover, grazing-controlled phytoplankton responds non-linearly to warming, depth and Pin value and its density may increase steeply with slight changes of these variables. Furthermore, BFF distribution determines grazer control of phytoplankton. However, the effect of such distribution depends on temperature, depth, Pin value and BFF density. In conclusion, this work shows that trophic control can strongly alter the response of eutrophication to warming. Therefore, the prediction of global warming effects must consider trophic interactions. In addition, this study shows the importance of interactions between abiotic and biotic factors, including spatial distribution, in eutrophication control.

CH4 and CO2 emitted from freshwaters are significant component of the global carbon cycle. While recent estimates paid special attention to flux rates of both gases from lakes and reservoirs, small and shallow ponds received less attention. Moreover, measured and modeled flux rates are subject to high uncertainty caused by low spatial and temporal measurement resolution. Using a continuous measurement approach of flux rates and weekly measurements of dissolved gaseous of CH4 and CO2 in a small and shallow pond in Southwest Germany, our results revealed high variability of flux rate for both gases within small (0.5m) spatial and short (1hour) temporal scales. The pond was characterized by high dissolved gas concentrations with partial pressures of CH4 ranging from 46 to 400 ppm and CO2 ranging between 620 and 4280 ppm. Ebullition was the major flux path for CH4 (80-fold higher than the diffusive flux), and varied between 0 and 32.5 mmol CH4 m-2 d-1. The observed strong variation of CH4 and CO2 fluxes within few meters and subdiurnal time scales, emphasizes the need for high flux measurement resolution.

RS03 – Presentation

Evaluating the invasion of Crassula helmsii on biodiversity at a site of national conservation importance

Non-native invasives (NNI) are a serious threat to aquatic ecosystems worldwide, with potential impacts for both biodiversity and economics. Crassula helmsii, an aquatic perennial plant originally from Australia is listed as one of the worst hundred European NNIs. It has steadily colonised different freshwater habitats across Europe since the 1950s when it was first recorded in the wild in England.
Evaluation of Crassula extent and specific impacts is critical to the assessment and potential mitigation of invasion. This includes: standardisation of methods for assessment of coverage; understanding the specific impacts at different spatial and temporal scales; and the availability of pre-invasion data to use as a baseline to aid interpretation of results. The Freshwater Biological Association, has collected worldwide freshwater data holdings over the last 80 years, an extremely valuable resource for baseline assessments. Use was made of this data during a survey of a tarn in the NW of England. This work was undertaken in the summer of 2016, to assess the coverage and potential impacts of Crassula (first recorded in 2010) on macrophyte biodiversity and other fauna of interest, at a site of conservation importance.
Despite its longstanding presence in Europe, there are still many unknown aspects to the ecology of this species. It is vital to understand them for the management, mitigation, control and eradication of Crassula. The aim of this paper is to open a discussion on utilising results from different studies to get a better understanding of the problem and ways forward to common solutions.

RS05 – Poster

Changing patterns in the littoral ecotone and potential factors in its decline in a northern English lake over a hundred-year perspective

Reedbed habitats dominated by stands of Common reed, Phragmites australis, are key areas of the littoral ecotone of lakes. During the last few decades, reedbeds have shown a significant decline throughout Europe, a trend that has also been observed on a local scale in lakes of the English Lake District.
Reedbeds provide a number of ecosystem services: microhabitats for algae and invertebrates, which are an important food source for other invertebrates as well as fish, mammals and water birds; provide physical protection of lake shores; help in carbon sequestration; have a role in nutrient cycling; and are a buffer between the terrestrial and the aquatic habitats. In addition, many of the species found living in, or associated with them, are of national and international importance.
The decline of these habitats has been attributed to many different factors such as: changes in land use; shoreline development; eutrophication; artificial changes in water levels; extreme hydrological events; and climate change. The results of some of these declines may be a loss of biodiversity as well as an impact on the water quality.
The aim of this paper is to verify and quantify reedbed retreat at Esthwaite Water (NW of England) over a hundred-year time-scale. The decline is analysed using an interdisciplinary approach, taking into account different scales of land use changes, as well as supplementary biological and physical data from the lake catchment. These results are focused on a local scale but contribute to a wider European discussion on the reedbed retreat itself.

SS05 – Presentation

UNDERSTANDING THE PRODUCTION OF TASTE AND ODOUR COMPOUNDS IN RESERVOIRS: A WATER INDUSTRY PERSPECTIVE

A consistent increasing trend in the occurrence of the taste and odour compounds Geosmin and 2-Methylisoborneol (MIB) have been observed in Welsh drinking water reservoirs since the beginning of the decade. These include bodies of variable water chemistry and catchment land use patterns, such as lowland agricultural areas and upland oligotrophic reservoirs with no history of cyanobacterial blooms. There are a number of issues with the removal of these compounds via water treatment, such as high chemical and power costs, sludge disposal, need for space and planning permission in protected areas. A double approach to manage this problem included a ‘bottom-up’ one, by investigating the origin of the problem to identify solutions, and a ‘top-down’ approach, by trialling existing reservoir management techniques such as destratification via stirrers and ultrasound to reduce targeted algal populations. This presentation will focus on case studies where the afore-mentioned approaches have been tested in a number of reservoirs in Wales. Preliminary findings include the production of MIB by planktonic Anabaena, the co-production of Geosmin and MIB by benthic Oscillatoria, the impact of a Resmix system on mass fluxes of both compounds and the unintended impacts of mixing to the dynamics of metals in one of the reservoirs.

SS12 – Poster

How intensity and frequency of flow intermittency affect organic matter decomposition in the surface and subsurface water in Mediterranean streams?

Climate change predicts a greater frequency of extreme events, including longer and more severe droughts that are expected to alter the hydrological regime in rivers, being the Mediterranean areas especially vulnerable. The decomposition of organic matter plays a fundamental role in ecosystem functioning. However, the consequences of flow alteration in this process due to climate change are highly uncertain. In this sense, the aim of this study is to analyse to which extent the intensity and frequency of flow intermittency affects the decomposition rate of organic matter in the subsurface (15 cm below stream bed) and surface water. To achieve this aim, wood sticks are placed for one year in the subsurface and surface water in 20 streams (with different intensity and frequency of flow intermittency) across Catalonia (NE Spain) to test the following hypotheses: (I) the decomposition rate in stream surface water are determined by the intensity and frequency of the flow intermittency; and (II) the decomposition rate in ephemeral rivers are faster in the subsurface water than in the stream surface water due to the fact that groundwater flow keeps humidity for a longer period of time. The results of this study will allow an ecological understanding to predict the effect of climatic change on ecosystem functioning in Mediterranean streams.

RS07 – Presentation

Sensitivity of laccase activity to the fungicide tebuconazole in decomposing litter

The present study investigates the sensitivity of laccase activity to the fungicide tebuconazole (TBZ) in order to seek for new functional toxicity descriptors in aquatic microbial communities associated to decomposing litter. With this aim, we analyzed the sensitivity of laccase from the different microbial components (fungi and bacteria growing separately and in co-existence), as well as that of their corresponding enzyme fractions (cell bound and diffusible), forming microbial communities in Alnus glutinosa leaves. Results show that fungi are pivotal for laccase in leaves and that their activity is repressed when they co-exist with bacteria. The sensitivity of laccase to TBZ was only detectable in leaves colonized by fungi separately (Alatospora acuminata populations), but absent in those colonized by bacteria alone and/or mixed fungi plus bacteria. Specifically, the increase of TBZ concentration enhances laccase in Alatospora acuminata populations but decreases ergosterol concentration as well as the amount of 18S RNA gene copies. This activity response suggests a detoxification mechanism employed by the fungus in order to reduce TBZ toxicity. Besides, enzyme fractioning showed that laccase activity in the cell bound fraction (76% of the total activity) was sensitive to the fungicide, but not that in the diffusible fraction (24% of total activity). Hence, TBZ would influence laccase activity in the presence of fungal cells but not in enzymes already synthesized in the extracellular space. The present study highlights the importance of the biological complexity level (i. e. population, community, ecosystem) when seeking for appropriate functional ecotoxicity descriptors in aquatic microbial communities.